I think the saving grace for his happiness is the live pothos plant I have growing out of the back of my tank. He hangs out in the roots most of the time resting. When he is hungry or bored he go's out in the tank.

WOW! What I couldn't give for a tank that size!! Just think of the possibilities.....giant Sorority anyone? I bet your boy is loving the extra space ;)

But keep an eye out....the Angels and Gouramis may go after your betta, or he may go after them.....or both. I think if your tank is pretty heavily planted then you should be alright, but just keep an eye out and remove him if you notice any aggression, ripped fins(on him or the other fish), or signs of stress from anyone.